n8gm

I recentlty bought a 2000 Grand Marquis with he handling package. When I bought the car the window sticker claimed 18 mpg city and 25 mpg highway. I have taken it on two long highway trips recently and the best I could do was about 18 mpg. Is this normal? Since I have owned the car, I noticed that when the car is in overdrive between 35 to 50 mph and I give it gas to accelerate but don't give it enough for the car to downsift the car will buck slightly until I make it down shift. Could these two issues be related? I have read that the Mass Air Flow (MAF) Sensor and Differential Pressure Feedback EGR (DPFE) Sensor are occasional problems with these cars. I am wondering if either of those sensors could be failing.

Crownvic_Dan

Yeah seems like your car should be doing better than 18 mpg highway.Whats the milage on iy?

laminge

Welcome to the site

Hope someone can help

n8gm

It has 48K miles on it. I am hesitant to take it back to the dealership to be looked at. I don't want to spend lots of time and money having them take a stab at diagnosing the problem only to come up with nothing.

Sid Post

I have a similar car to yours. It will punish me if I am a lead foot.

Recently my car started loosing MPG (~2MPG) in both City and Highway driving. I ran some fuel injector cleaner through it and replace the air filter and things are back to normal. I am back up to 24 consistently at 80MPH steady state. I still haven't beat the 25.4MPG I routinely got when it was just a year old though. City mileage runs about 22.8MPG again like it should in mixed use driving (stop and go and steady 45MPH).

n8gm

I will give the injector cleaner a try and check my air filter.

LunaticSVT

Another thing to check is the leads for wear and check the plugs for fouling.